Over the past several decades, radar systems have been implemented in a broad range of applications for detecting target objects such as vehicles and airplanes. More recently, radar systems have been implemented in automobiles. Automotive radar systems have been developed for helping drivers to park their cars, to follow traffic at a safe distance, and to detect driving obstacles. For example, when an automotive radar system detects an obstacle or slowing traffic in front of the vehicle, the system may issue an audio and/or visual warning to the driver, such as in the form of an audible tone or a visible warning light. The system may also exercise active control over the vehicle, such as by applying the brakes, in order to avoid an accident.
A radar system may detect the range (e.g., distance) to a target object by determining the roundtrip delay period between the transmission of a radar signal and the receipt of the signal returning back to the radar antenna after it bounces off of the target object. This round-trip delay, divided in half and then multiplied by the speed of the signal radiation, gives the distance between the radar antenna and the target object, assuming the transmitting antenna and the receiving antenna of the system are the same antenna or are very close to each other.
In addition to detecting the range to a target object, a radar system may be used to detect the direction of a target object as expressed in terms of the target object's elevation angle, azimuth angle, and range relative to the radar antenna. Such direction detection is commonly achieved using a monopulse radar system having four channels for facilitating either amplitude-comparison monopulse (wherein the beams emitted by the four channels of the radar system are squinted) or phase-comparison monopulse (wherein the beams emitted by the four channels of the radar system are not squinted), or three channels if two channels are compared to a common base channel. By comparing the magnitudes for magnitude-comparison monoplulse or the phases for phase-comparison monopulse of the beams reflected off of a target object, the elevation angle and azimuth angle of the target object may be derived.
Conventional four-channel monopulse radar systems with three-dimensional detection are generally implemented using one of four different configurations. For example, referring to FIG. 1A, a four-channel monopulse radar system configuration is shown that includes a common transmitting channel TX and four receiving channels RX1-4 disposed in a 2×2 arrangement in the x and y directions. Referring to FIG. 1B, a system configuration is shown that includes one common receiving channel RX and four transmission channels TX1-4 disposed in a 2×2 arrangement in the x and y directions. Referring to FIG. 1C, a system configuration is shown that includes two transmitting channels TX1 and TX2 disposed in a side-by-side arrangement in the x direction and two receiving channels RX1 and RX2 disposed in a side-by-side arrangement in the y direction. Referring to FIG. 1D, a system configuration is shown that includes two transmitting channels TX1 and TX2 disposed in a stacked arrangement in the y direction and two receiving channels RX1 and RX2 disposed in a side-by-side arrangement in the x direction.
While four-channel monopulse radar systems are generally effective for determining the elevation and azimuth angles of target objects, the antenna and circuitry requirements of such systems can make them too large and too costly for practical implementation in automobile applications. Moreover, four-channel systems can present long detection times if the channels of a system are operated in series. It would therefore be desirable to provide a monopulse radar system for automobile applications that can be implemented in a compact volume and at a low cost.